1. Field of the Invention
The present invention relates to an electron emission device used in a so-called field emission type display apparatus, a production method of the electron emission device, and a display apparatus using the electron emission device.
2. Description of the Prior Art
Recently, the development of display devices has been directed to make the devices thinner. To achieve this special attention has been paid to, a so-called field emission type display (hereinafter, referred to as FED).
As shown in FIG. 1, in an FED, for one pixel, there are provided a spindt type electron emission device 100 and a fluorescent panel 101 formed opposite to this electron emission device 100. Such pixels are formed in a matrix to constitute a display.
The portion corresponding to one pixel includes an electron emission device 100 having: a cathode electrode 103 formed on a cathode panel 102; an insulation layer 104 formed on the cathode electrode 103; a gate electrode 105 layered on this insulation layer 104; a hole portion 106 formed through the gate electrode and the insulation layer 104; and an electron emission emitter 107 formed inside the holde portion 106. Moreover, this FED includes a fluorescent plane 101 arranged so as to oppose the electron emission device 100 and having a front panel 108, an anode electrode 109 formed on this front panel 108, and a fluorescent body 110. Furthermore, this FED is constituted so that a predetermined voltage is applied to the cathode electrode 103, the gate electrode 105, and the anode electrode 109.
In this FED, the electron emitter 107 is made from material such as W, Mo, and Ni processed approximately into a small conical shape with its tip positioned at a predetermined distance from the gate electrode. This electron emission device 100 emits electrons from the tip of the electron emitter 107 and includes a number of the electron emitters 107.
In the FED having such a configuration, a predetermined electric field is generated between the cathode electrode 103 and the gate electrode 105. This causes electrons to be emitted from the tip of the electron emitter 107. The electrons emitted strike the fluorescent body 110 formed on the anode electrode 109. This excites the fluorescent body 110 to emit light. The FED controls the quantity of the electrons emitted from the electron emitter 107 for each pixel to display a desired image.
More specifically, in the FED, the hole portion 106 has an opening dimension of about 1 micrometer or less; and the electron emitter 107 has a height of 1 micrometer or less and the base of electron emitter 107 has a curvature radius in the order of several tens of nm. Moreover, in the FED, one pixel has several tens to several thousands of electron emitters 107. For example, in a display of XGA class in which the number of pixels is 1024xc3x97768xc3x97 (RGB), it is necessary to provide 100 to 100000 millions of electron emitters 107.
A voltage of several tens of volts is applied from the cathode electrode 103 to the gate electrode 105, so as to generate an electric field in the order of 107 V/cm between the gate electrode 105 and the tip of the of the electron emitters 107. Moreover, a voltage on the order of 200 to 5000 V is applied to the anode electrode 109, so that electrons emitted from the electron emitter 107 strike the fluorescent plane 101.
However, the FED described above having the electron emitters 107 of the spindt type has problems as follows.
First of all, the spindt type electron emitter 107 is formed on a microscopic scale, requiring a submicron accuracy. Accordingly, it is necessary to employ a process and apparatus identical to those for producing an integrated circuit (IC) to form the FED. However, for example, when preparing a display having a screen of 17-inch size in a diagonal direction, the apparatus size becomes too large, significantly increasing the costs. Besides, if the display is to have a large size, the production yield is remarkably lowered because the electron emitters 107 need be formed uniformly over the entire cathode panel surface.
Secondly, the electron emitter 107 is made from a material such as W, Mo, and Ni, and an electric field in the order of 107 V/cm is required between the cathode electrode 103 and the gate electrode 105. In order to satisfy these parameters while maintaining the small voltage applied, the interval between the gate electrode 105 and the electron emitter 107 must be a submicron or less. However, it is quite difficult to form a submicron interval without short-circuiting the gate electrode 105 and the cathode electrode 103. Thus, the production yield is significantly lowered.
Thirdly, the material W, Mo, or Ni constituting the electron emitters 107, for example, is eroded by the collision of ions generated from a residual gas and from the fluorescent body 110 and is rapidly deteriorated. Thus, in the FED having this spindt type electron emitter 107, the vacuum degree of the portion containing the electron emitter 107 must be reduced. More specifically, it is necessary to maintain a vacuum 10 times lower than the vacuum degree of an ordinary cathode ray tube 10xe2x80x3 to 10xe2x88x927 Torr. In order to reach such a low vacuum, it is necessary to greatly increase the mechanical strength of the display, preventing reduction in the apparatus size including the thickness and weight.
In contrast to this spindt type electron emitters 107, a there has been suggested an electron emission device including an electron emitter of conductive fine particle type. An electron emission device including this conductive fine particle type electron emitter is disclosed, for example, in PCT/GB96/01858 [1] and WO 97/06549 [2], wherein conductive fine particles are contained in a dielectric layer, i.e., the conductive fine particles are covered with a dielectric layer so as to be arranged via the dielectric layer onto a conductive layer.
This conductive fine particle type electron emitter generates an electric field when a voltage is applied to the conductive layer. This electric field causes the conductive fine particles to emit electrons. In this case, the electron emitter can be formed easier than the aforementioned spindt type and is appropriate for a large-screen flat display that can be produced with a reasonable production cost.
Moreover, U.S. Pat. No. 5,608,283 [3] discloses an electron emission device including a conductive fine particle type electron emitter wherein conductive fine particles are provided on a high-resistance pillar formed on a conductive layer and on the conductive layer via a bonding layer.
This electron emitter also generates an electric field so that the conductive fine particles arranged on the bonding layer, and the like, emit electrons. In this case also, the electron emitter can be produced easier than the aforementioned spindt type and is appropriate for a large-screen flat display that can be produced at a reasonable cost.
On the other hand, in the electron emission device disclosed in Documents [1] and [2], it is necessary to accurately define the thickness of the dielectric layer between the conductive fine particles and the conductive layer as well as the thickness of the dielectric layer covering the conductive fine particles. More specifically, each of these thickness values should be on the order of {fraction (1/10)} to {fraction (1/100)} of the conductive fine particle diameter, i.e., several hundreds Angstroms.
However, it is quite difficult to control the thickness of the dielectric layer on the order of several hundreds of Angstroms. In this electron emission device, if it is impossible to control the thickness of this dielectric layer with a high accuracy, it is impossible to selectively emit electrons, thereby preventing use of the device as a display for displaying an image. That is, such an electron emission device having a difficulty in controlling the thickness of the dielectric layer cannot be used for an image display apparatus such as the FED.
Moreover, in the electron emission device as disclosed in Document [3], conductive fine particles are arranged so as to be fixed by the bonding layer. In this electron emission device, if the conductive fine particles are covered by the bonding layer, emission of electrons is disabled. In order to form a bonding layer without covering the conductive fine particles, it is necessary to control the thickness of the bonding layer to be several hundreds of Angstroms.
However, it has been difficult to control the thickness of the bonding layer to several hundreds of Angstroms. In such an electron emission device, because of the difficulty to controlling the thickness of the bonding layer with a high accuracy, the conductive fine particles may be embedded into the bonding layer, preventing the reliable emission of electrons.
It is therefore an object of the present invention to solve the aforementioned problems of the aforementioned conventional electron emission device so as to provide an electron emission device capable of assuring emission of electrons without requiring the control of the film thickness on a submicron scale, and a production method of such an electron emission device as well as a display apparatus using the electron emission device.
The electron emission device that solves the aforementioned problem includes a cathode electrode of conductive fine particles formed on a substrate,
wherein the conductive fine particles are adhered directly onto the substrate and electrons are emitted from the conductive fine particles when a predetermined electric field is applied.
In this electron emission device, generation of an electric field causes the conductive fine particles to emit electrons. In this electron emission device, the conductive fine particles are adhered directly onto the substrate. Accordingly, this electron emission device does not require an adhesive layer or the like for fixing the conductive fine particles onto the substrate. Consequently, this electron emission device has a configuration such that the conductive fine particles can easily emit electrons.
Moreover, in the electron emission device according to the present invention, it is preferable that those portions of the conductive fine particles adhered directly onto the substrate are held by a glass material.
In this case, the electron emission device has the conductive fine particles which are firmly fixed by the glass material onto the substrate. This can prevent peeling off of the conductive fine particles from the substrate.
On the other hand, the electron emission device production method according to the present invention includes: a step of applying a conductive paint containing conductive fine particles and binder onto a substrate to form a film there; and a step of sintering the conductive paint film formed on the substrate, so as to remove the binder, thus adhering the conductive fine particles directly onto the substrate.
In this electron emission device production method, the conductive paint film is sintered to remove a binder contained in the conductive paint film. Thus, the conductive fine particles can be adhered to the substrate by the Van der Waals force. Accordingly, the conductive fine particles can be firmly fixed to the substrate. That is, this method does not require formation of an adhesive layer for fixing the conductive fine particles onto the substrate. Moreover, in this method, because there is no need to form an adhesive layer or the like, the conductive fine particles need not be covered.
Moreover, in the electron emission device production method according to the present invention, it is possible to carry out a surface treatment after removing the binder by sintering.
In this case, the surface treatment of the conductive fine particles can remove impurities such as a binder completely from the surfaces of the conductive fine particles. Moreover, the conductive fine particles after being subjected to the surface treatment have exposed portions activated.
Furthermore in the electron emission device production method according to the present invention, the conductive paint may contain a glass material, and the conductive paint applied onto the substrate is sintered to remove the binder, so that the conductive fine particles are adhered directly onto the substrate and the glass material contained in the conductive paint film is precipitated so as to hold portions of the conductive fine particles adhered directly onto the substrate.
In this case, the conductive paint film containing the glass material is sintered to remove the binder and the like and settle the glass material onto the substrate. In this method, the settled glass material covers the adhesion portion of the conductive fine particles. This further fixes the conductive fine particles firmly onto the substrate.
Furthermore, the display apparatus according to the present invention includes: an electron emission device including a cathode electrode having a plurality of conductive fine particles arranged on a substrate; an anode electrode arranged to oppose the electron emission device so as to generate an electric field to accelerate electrons emitted from the electron emission device; and a fluorescent plane arranged on the anode electrode to be struck by electrons accelerated by the anode electrode. In this display apparatus, the cathode electrode has the plurality of conductive fine particles adhered directly onto the substrate and emits electrons when a predetermined electric field is present and the electrons emitted from the cathode electrode cause the fluorescent plane to emit light.
In the display apparatus having the aforementioned configuration according to the present invention, electrons are emitted from the conductive fine particles adhered directly onto the substrate. In this display apparatus, the electrons thus emitted are accelerated by the electric field generated by the anode electrode to strick the fluorescent plane. This causes the fluorescent plane to emit light, to display an image.